Link broken

[gurry]

The link "improved error messages" on this page is broken. The problem is due the underlying URL being this:

https://rust-lang-nursery.github.io/edition-guide/rust-2018/the-compiler/rust-2018/the-compiler/improved-error-messages.html

instead of this:
https://rust-lang-nursery.github.io/edition-guide/rust-2018/the-compiler/index.html

[xonatius]

Same for other pages, for example Module system. Looks like links from 419edb8 need to be fixed.

[ehuss]

Links should now be fixed as of #152.